This invention concerns a cyclically operating pressure-swing absorption apparatus and process for purifying and separating gases by operating a plurality of adsorbers having their respective intake ends connected to a raw gas line, and their respective exhaust ends connected to the product gas line by means of valve controlled pipelines. The adsorbers are also mutually interconnected through valve-equipped pressure balancing lines or purge lines.
This invention is particularly applicable to pressure-swing adsorption processes having up to 12 adsorbers for purifying and decomposing gases, e.g., German Offenlegungsschrift No. 26 24 346. In the prior art apparatus six valves are used to control each adsorber, with two valves operating as simple on-off valves (intake and exhaust valves), and four operating as control valves for the different operating stages.
In the prior art process, raw gas passes through an intake valve into an adsorber wherein the more easily adsorbed components are retained, and the components which are more difficult to adsorb leave the apparatus as the product gas flow through an exhaust valve. The adsorption stage occurs at a higher pressure, and is followed by several expansion stages by means of which the product gas and the adsorbed components located in the interstices of the adsorbent are released. The first expansion steps are carried out by a pressure-balancing process, through the corresponding control valves with other adsorbers at lower pressures which are thereby raised to a specified higher pressure. The gas obtained in the last expansion stage of each adsorber is evacuated as the residual gas. This process stage in each adsorber is followed by a counterflow purging for the purpose of removing all adsorbed components from the adsorbent. Finally, several pressure build-up steps occur primarily by means of pressure balancing through control valves with other adsorbers at higher pressures, wherein the last pressurization to the adsorption pressure occurs through the intake valve by using a partial flow of the product gas.
The period of time in operation is often only a few seconds. Thus, the type of control valves used are extremely important for the purpose of achieving such short operational times. Each of these valves is controlled by respective individual electrical signal. More specifically, involved are in analog current signal source, an electrical signal line for analog current signals, and transducer means for converting the electrical analog current signals into pneumatic signals for the purpose of controlling the operation of the pneumatic valves. As applied to the prior art conventional 9-bed pressure varying adsorption apparatus having 36 control valves, such a solution requires that 36 of the above-described device combinations be provided for controlling the opening and closing of all of the valves. This results in increased costs and a high probability of operational defects.